Gas hydrate production apparatus

ABSTRACT

The invention provides a gas hydrate production apparatus which can eliminate the need for an agitator in a generator, and at the same time, can make constant the percentage of gas hydration of the product. A shell-and-tube-type generator  2  is provided downstream of an ejector-type mixer  1  that stirs and mixes a raw-material gas g and a raw-material water w. In addition, partition walls  41  to  43  each causing a gas hydrate slurry to turn around are provided in each of end plates  37  and  38  placed respectively in the front and rear ends of the generator  2 . Moreover, a dehydrator  3  including a cone-shaped filter  48  is provided downstream of the generator  2 , and a drainage pipe  11  is provided to the dehydrator  3 . Further, a flow regulating valve  12  is provided to the drainage pipe  11.

TECHNICAL FIELD

The present invention relates to a gas hydrate production apparatus thatproduces a gas hydrate by causing a raw-material gas, such as a naturalgas, to react with water.

BACKGROUND ART

A gas hydrate is ice-like solid crystals formed of water molecules andgas molecules, and is a generic term referring to clathrate hydrates(hydrates) in each of which each gas molecule is included inside a cageconstructed of water molecules with a three-dimensional structure. Thegas hydrate has been actively studied and developed as transportationand storage means for natural gases because the gas hydrate contains anatural gas in an amount as large as approximately 165 Nm³ per 1 m³ ofthe gas hydrate.

As apparatuses for producing gas hydrates, there have conventionallybeen the following systems: a bubbling system (see, for example,Japanese patent application Kokai publication No. 2003-80056) in which araw-material gas is blown into a raw-material water in a generator; aspray system (see, for example, Japanese patent application Kokaipublication No. 2002-38171) in which a raw-material water is sprayedinto a generator filled with a raw-material gas; a tubular reactorsystem (see, for example, Japanese patent application Kokai publicationNo. 2002-356685) using a line mixer and a water-tube-type tubularreactor; and the like.

However, the bubbling system has the following problems and the likebecause the bubbling system includes: a generator with an agitator; anexternal cooler that removes a generated heat (called also a reactionheat); a gravity dehydrator (called also a gravity dehydrating tower) inwhich a gas hydrate slurry, generated by the generator and thenintroduced thereinto, is dehydrated by utilizing gravity so that anunreacted water is removed therefrom. Specifically, (1) the bubblingsystem requires the agitator, (2) the bubbling system requires twodevices, that is, the generator and the external cooler, (3) thedehydrator is large in size because of the gravity dehydration, and (4)the dehydrator is difficult to control because of the gravitydehydration.

Meanwhile, the spray system has the following problems and the likebecause water is sprayed from a nozzle into the generator filled with araw-material gas. Specifically, (1) the speed of producing a gas hydrateis slow, and (2) the cooling of a raw-material gas in the generator withthe external cooler is associated with a poor heat transmission.

On the other hand, the tube system has the following problems and thelike. Specifically, (1) the tubular reactor is long, and (2) a pressuredrop is large because of the long tubular reactor.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a gas hydrateproduction apparatus with no need for an agitator in a generator andwith a simple structure, as well as with easy control of a dehydratorand with capability of making constant the percentage of gas hydrationof the product.

Means for Solving the Problems

A gas hydrate production apparatus according to the invention as recitedin claim 1 is characterized by including: an ejector-type mixer thatstirs and mixes a raw-material gas and a raw-material water; ashell-and-tube-type generator provided downstream of the ejector-typemixer; partition walls provided in end plates placed respectively in thefront and rear ends of the generator, the partition walls each causing agas hydrate slurry to turn around; a dehydrator provided downstream ofthe generator, the dehydrator including a cone-shaped filter; a drainagepipe provided to the dehydrator; and a flow regulating valve provided tothe drainage pipe.

A gas hydrate production apparatus according to the invention as recitedin claim 2 is characterized by including: an ejector-type first mixerthat stirs and mixes a raw-material gas and a raw-material water; ashell-and-tube-type first generator provided downstream of theejector-type first mixer, the first generator intended to generate gashydrate cores; an ejector-type second mixer provided downstream of thefirst generator, the second mixer mixing the raw-material gas into aslurry containing the gas hydrate cores, and then stirring and mixingthe raw-material gas and the slurry; a second generator provideddownstream of the second mixer, the second generator intended togenerate a gas hydrate; and a flow regulating valve provided to a pipethrough which a part of the gas hydrate slurry generated by the secondgenerator is returned to the second mixer.

The invention as recited in claim 3 is characterized in that, in the gashydrate production apparatus as recited in claim 2, partition walls areprovided in each of end plates placed respectively in the front and rearends of each of the first and second generators, the partition wallseach causing the slurry to turn around.

The invention as recited in claim 4 is characterized in that, in the gashydrate production apparatus as recited in claim 1 or 3, corner portionsare provided among joint portions of each end plate and thecorresponding partition walls, the corner portions each having a curvedwettable surface.

The invention as recited in claim 5 is characterized in that, in the gashydrate production apparatus as recited in claim 1 or 2, first collisionbodies and second collision bodies are provided alternately in anarrowly constricted body portion of each ejector type mixer, the firstcollision bodies each being a plate-shaped base plate provided withtriangular or trapezoidal penetrating portions radially formed therein,the second collision bodies each being a plate-shaped base plateprovided with a stellate penetrating portion formed therein.

The invention as recited in claim 6 is characterized in that, in the gashydrate production apparatus as recited in claim 1, a part of the gashydrate slurry generated by the generator is returned and recirculatedto the generator.

The invention as recited in claim 7 is characterized in that, in the gashydrate production apparatus as recited in claim 2, a part of the gashydrate slurry generated by the first generator is returned andrecirculated to the first generator.

EFFECTS OF THE INVENTION

As described above, in the invention according to claim 1, theraw-material gas and the raw-material water are stirred and mixed by theejector-type mixer. Accordingly, the invention eliminates the need foran agitator in a generator, a motor for driving such agitator, and thelike. As a result, the structure is simplified and no electric power fordriving a motor is required.

In addition, in the invention, the shell-and-tube-type generator isprovided downstream of the ejector-type mixer and the partition wallseach causing the gas hydrate slurry to turn around are provided in theend plates placed respectively in the front and rear ends of thegenerator. Accordingly, the invention makes the generator compact ascompared to the conventional tubular reactor system including aplurality of bent tubes, and thus makes it possible to suppress apressure drop in the generator. Moreover, since the generator is of theshell-and-tube type, the generator is capable of efficiently removing areaction heat generated during the generation of a gas hydrate, andtherefore, is capable of efficiently generating a gas hydrate.

Further, in the invention, the dehydrator including the cone-shapedfilter is provided downstream of the generator, and the flow regulatingvalve is provided to the drainage pipe of the dehydrator. Accordingly,the invention facilitates the control on the dehydrator, and thus makesit possible to control the percentage of gas hydration (hereinafter,called an NGH percentage) of a gas hydrate as a product.

The percentage of gas hydration herein means a weight ratio of a hydrateof theoretical values to the weight of a sample.

        [Mathematical  Formula  1]$H = {100 \times \frac{\left( {W_{1} - W_{2}} \right) \times \left\{ {1 + {N \times {{Mw}/{Mg}}}} \right\}}{W_{1}}}$

H: Percentage of Gas Hydration (%) W₁: Weight of Sample (g) W₂: Weightof Water Constituting Hydrate (g) Mw: Molecular Weight of Water Wg:Molecular Weight of Gas N: Hydration Number

In the invention according to claim 2, as described above, the secondgenerator intended to generate a gas hydrate is provided downstream ofthe shell-and-tube-type first generator intended to generate gas hydratecores, and further, the flow regulating valve is provided to the pipethrough which a part of the gas hydrate slurry generated by the secondgenerator is returned to the second mixer. Accordingly, the inventionmakes it possible not only to increase the particle size of the gashydrate but also to control the NGH percentage.

In addition, the invention eliminates, in the same manner as that of theinvention according to claim 1, the need for an agitator in a generator,a motor for driving such agitator, and the like. Further, the inventionmakes the generator compact as compared to the conventional tubularreactor system including a plurality of bent tubes, and thus makes itpossible to suppress a pressure drop in the generator. Moreover, sincethe generator is of the shell-and-tube type, the generator exerts theeffect of efficiently removing a reaction heat, and the like.

In the invention according to claim 3, the partition walls each causingthe slurry to turn around are provided in the end plates placedrespectively in the front and rear ends of each of the first and secondgenerators. Accordingly, the invention makes it possible to elongate thegas hydrate generating region with no increase in pressure drops in thefirst and second generators, and accordingly, makes it possible topromote the generation of gas hydrate cores and the growth of particlesof the gas hydrate.

In the invention according to claim 4, the corner portions each havingthe curved wettable surface are provided among the joint portions ofeach end plate and the corresponding partition walls. Accordingly, theinvention makes it possible to make uniform the flow rate of the gashydrate slurry in each end plate.

In the invention according to claim 5, the first collision bodies andthe second collision bodies are alternately provided in the narrowlyconstricted body portion of the ejector-type mixer. Here, each firstcollision body is a plate-shaped base plate provided with triangular ortrapezoidal penetrating portions formed therein, and each secondcollision body is a plate-shaped base plate provided with a stellatepenetrating portion formed therein. Accordingly, the raw-material wateris intensively stirred by the first and second collision bodies, and theraw-material gas is involved into the raw-material water and crushedinto fine bubbles therein, so that the raw-material water and theraw-material gas are mixed with each other. In this way, the area ofcontact between the raw-material gas and the raw-material water isincreased. As a result, the raw-material gas is efficiently dissolvedinto the raw-material water.

Consider the case where a part of the gas hydrate slurry generated bythe generator is returned and recirculated to the generator, as in theinvention according to claim 6. In this case, since the hydrate coresare present in the gas hydrate slurry, the gas hydrate is generated atthe operating temperature with no need for a supercooling process.

On the other hand, in the case where no recirculation is performed, amixture of the water and gas discharged from the mixer is caused toenter a shell-and-tube heat exchanger and is thus cooled therein.However, the hydrate is not generated until the temperature reaches arange where the degree of supercooling has a certain value (4 to 8° C.).In addition, once the degree of supercooling reaches the value, thehydrate is rapidly generated, and the temperature is decreased to thetemperature of the steady operation. If the hydrate is rapidly generatedin this way, the inside of the tubes is sometimes blocked by thehydrate. Moreover, since the amount of heat transmission is decreased inthe supercooling section, the apparatus has to be increased in size.

The degree of supercooling is a difference between a generationtemperature for the hydrate and an equilibrium temperature betweengeneration and decomposition at the generation pressure for the hydrate,and is expressed by the following formula.

ΔT=Te−Tf  [Mathematical Formula 2]

Here, ΔT: Degree of Supercooling [K]; Te: Equilibrium Temperature atGeneration Pressure [K]; Tf: Generation Temperature [K].

Also in the case where a part of the gas hydrate slurry generated by thefirst generator is returned and recirculated to the first generator, asin the invention according to claim 7, the same effects as describedabove are obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configurational diagram of a gas hydrateproduction apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a mixer.

FIG. 3 is a cross-sectional view of a mixer.

Part (a) of FIG. 4 is a front view of a first collision body, and Part(b) of FIG. 4 is a front view of a second collision body.

FIG. 5 is a partially cross-sectional side view of a generator.

Part (a) of FIG. 6 is a cross-sectional view taken along a line X-X inFIG. 5, and Part (b) of FIG. 6 is a cross-sectional view taken along aline Y-Y in FIG. 5.

FIG. 7 is a cross-sectional view of an end plate.

FIG. 8 is a schematic configurational diagram of another embodiment ofthe gas hydrate production apparatus according to the present invention.

EXPLANATION OF REFERENCE SIGNS

-   g raw-material gas-   s gas hydrate slurry-   w raw-material water-   1 ejector-type mixer-   2 shell-and-tube-type generator-   3 dehydrator-   11 drainage pipe-   12 flow regulating valve-   37, 38 end plate-   41, 42, 43 partition wall-   48 filter

BEST MODES FOR CARRYING OUT THE INVENTION

First, a first embodiment will be described, and then, a secondembodiment will be described.

(1) First Embodiment

A gas hydrate production apparatus of the present invention includes, asillustrated in FIG. 1, an ejector-type mixer 1, a shell-and-tube-typegas hydrate generator 2, and a dehydrator 3. A raw-material gas supplypipe 4 and a raw-material water supply pipe 5 are connected to the mixer1. Further, the mixer 1 and the gas hydrate generator 2 are connected toeach other by a pipe 6. The gas hydrate generator 2 and the dehydrator 3are connected to each other by a slurry supply pipe 8 including a slurrypump 7.

The slurry supply pipe 8 is branched at a branching point a locatedbetween the slurry pump 7 and the dehydrator 3, and is thus configuredso that apart of the slurry is injected into the pipe 6 through a branchpipe 16. The amount of slurry to be circulated may be approximately 0 to10%. In addition, an NGH percentage meter 10 is provided to a gashydrate discharge pipe 9 that is provided at an outlet of the dehydrator3. Moreover, a flow regulating valve 12 and a pump 13 are provided to adrainage pipe 11 that connects the dehydrator 3 and the raw-materialwater supply pipe 5. Further, a compressor 15 is provided to anunreacted-gas recovery pipe 14 that connects the dehydrator 3 and theraw-material gas supply pipe 4.

Here, the flow regulating valve 12 is controlled by means of the NGHpercentage meter 10. As the NGH percentage meter, a mixing-ratiomeasurement system for a mixed-phase fluid (see Japanese patentapplication Kokai publication No. Sho 62-172253) or the like may beemployed, for example.

As illustrated in FIG. 2, the ejector-type mixer 1 is formed of: atubular body 21 that has a narrowly constricted body portion 20; and anozzle 23 that is located upstream of the body portion 20 and has anozzle tip 22 bent in an L-shape and located at an inlet of the bodyportion 20. Here, the raw-material water supply pipe 5 is connected toan upstream end of the tubular body 21, the pipe 6 is connected to adownstream end of the tubular body 21, and the raw-material gas supplypipe 4 is connected to the nozzle 23.

Although there is no problem with the ejector-type mixer illustrated inFIG. 2, first collision bodies 25 and second collision bodies 26 may bealternately provided in the narrowly constricted body portion 20 asillustrated in FIG. 3, which make it possible to further promote themixing of the raw-material gas and the raw-material water. Each of thefirst collision bodies 25 is, as illustrated in Part (a) of FIG. 4, acircular base plate 27 provided with triangular or trapezoidalpenetrating portions 28 radially formed therein. Each of the secondcollision bodies 26 is, as illustrated in Part (b) of FIG. 4, a circularbase plate 29 provided with a stellate penetrating portion 30 formedtherein. In this case, each first collision body 25 and each secondcollision body 26 are arranged in such a manner that one of the firstand second collision bodies 25 and 26 is rotated slightly in a clockwisedirection or a counterclockwise direction so that the penetratingportions 28 and 30 should not overlap each other.

As illustrated in FIG. 5, the shell-and-tube-type gas hydrate generator2 includes a body portion 32 incorporating a plurality of tubes 31. Theopposite ends of each tube 31 penetrate tube plates 33, 33 that tightlyclose the opposite ends of the body portion 32, respectively. The bodyportion 32 includes partition plates 34 provided alternately on aceiling portion and a bottom portion of the body portion 32, so that acoolant fluid that has flowed thereinto from a coolant inflow portion 35meanders and moves therein to be discharged from a coolant outflowportion 36.

The gas hydrate generator 2 includes a first end plate 37 in a front endportion (an upstream portion) of the body portion 32 and includes asecond end plate 38 in a rear end portion (a downstream portion) of thebody portion 32. The first end plate 37 includes a processed-targetinflow portion 39 in a bottom portion thereof. The second end plate 38includes a processed-target outflow portion 40 in an upper portionthereof.

Inside the first endplate 37, as illustrated in Part (a) of FIG. 6, aplurality of (for example, 10) sections A to J are formed by a pluralityof (for example, 5) partition walls 41 horizontally provided. In theembodiment, each pair of the sections B and C, the sections D and E, thesections F and G, and the sections H and I, which are each situated onthe right and left sides, communicate with each other.

On the other hand, inside the second end plate 38, as illustrated inPart (b) of FIG. 6, a vertical partition wall 42 extending from asection A′ to a section J′ is provided at the center, and partitionwalls 43 are provided between the section A′ and a section C′, betweensections D′ and G′, between a section H′ and the section J′, betweensections B′ and E′, and between sections F′ and I′, respectively.

Here, as illustrated in FIG. 7, corner portions 45 each having a curvedwettable surface 44 are provided among the joint portions of the firstend plate 37 and the partition walls 41 as well as the joint portions ofthe second end plate 38 and the partition walls 42 and 43 so that nodead zone for water should be formed therein.

The dehydrator 3 is, as illustrated in FIG. 1, formed of apressure-tight container 47 and a cone-shaped (a conical frustum-shaped)filter 48 provided substantially horizontally in the pressure-tightcontainer 47. The filter 48 has been subjected to mesh processing. Inaddition, the drainage pipe 11 is connected to a bottom portion of thepressure-tight container 47, while the unreacted-gas recovery pipe 14 isconnected to an upper portion of the pressure-tight container 47. Itshould be noted that, as needed, a cone-shaped screw (not illustrated)may be provided inside the filter 48, thereby increasing the force tothrust the gas hydrate slurry. Moreover, the dehydrator 3 may be one inwhich the filter 48 is provided in an upright posture.

Next, the operation of the above-described gas hydrate productionapparatus will be described.

As illustrated in FIG. 2, a raw-material water w that has been cooled toa predetermined temperature (for example, 4 to 8° C.) is supplied to thetubular body 21 of the mixer 1, and a raw-material gas g that has beenpressurized up to a predetermined pressure (for example, 4 to 5.5 MPa)is supplied to the nozzle 23 of the mixer 1. In this event, the flowrate is drastically increased in the narrowly constricted body portion20 of the tubular body 21. Accordingly, the raw-material gas g is formedinto fine bubbles, which are then mixed uniformly with the raw-materialwater w.

A mixed water w′ into which the raw-material gas has been mixed flowsthrough the pipe 6 to be supplied to the processed-target inflow portion39 of the shell-and-tube-type gas hydrate generator 2, as illustrated inFIG. 1. The mixed water w′ thus supplied to the processed-target inflowportion 39 of the shell-and-tube-type gas hydrate generator 2 is, asillustrated in FIG. 5, caused to turn around along each of the partitionwalls 41 inside the first end plate 37 and the partition walls 42 and 43inside the second end plate 38, thereby meandering many times in thebody portion 32. The mixed water w′ is eventually discharged from theprocessed-target outflow portion 40. While the mixed water w′ flows, theraw-material gas g and the raw-material water w react with each other toform a gas hydrate slurry s.

Here, the flow of the mixed water w′ in the first end plate 37 and thesecond end plate 38 will be described. In the first end plate 37, asillustrated in Part (a) of FIG. 6, the mixed water w′ flows from thesection B to the section C, from the section D to the section E, fromthe section F to the section G, and from the section H to the section I.In the second end plate 38, as illustrated in Part (b) of FIG. 6, themixed water w′ flows from the section A′ to the section B′, from thesection C′ to the section D′, from the section E′ to the section F′,from the section G′ to the section H′, and from the section I′ to thesection J′.

The gas hydrate slurry s (having an NGH percentage of 20 to 30%)generated by the gas hydrate generator 2 is, as illustrated in FIG. 1,supplied to the dehydrator 3 by the slurry pump 7. The gas hydrateslurry s supplied to the dehydrator 3 is pressurized and thus dehydratedby the thrust force of the slurry pump 7 because the filter 48 is formedin the cone shape. As a result, the gas hydrate slurry s is formed intoa gas hydrate n having an NGH percentage of approximately 40 to 60%.

An unreacted water w″ generated through the dehydration by thedehydrator 2 is returned to the raw-material water supply pipe 5 by thepump 13. In this event, the NGH percentage can be controlled byadjusting the flow regulating valve 12 by means of the NGH percentagemeter 10 provided to the gas hydrate discharge pipe 9. On the otherhand, an unreacted gas g″ accumulated in the dehydrator 3 is returned tothe raw-material gas supply pipe 4 through the unreacted-gas recoverypipe 14.

Next, a second embodiment will be described.

(2) Second Embodiment

In a gas hydrate production apparatus of this embodiment, as illustratedin FIG. 8, a shell-and-tube-type first generator 53 intended to generategas hydrate cores is provided downstream of an ejector-type first mixer51 with a first pipe 52 interposed therebetween, the first mixer 51stirring and mixing a raw-material gas g and a raw-material water w.Further, an ejector-type second mixer 55 is provided downstream of thefirst generator 53 with a second pipe 54 interposed therebetween.Moreover, a second generator 57 intended to generate a gas hydrate isprovided downstream of the second mixer 55 with a third pipe 56interposed therebetween.

Furthermore, a gas hydrate slurry discharge pipe 58 provided to thesecond generator 57 and the second pipe 54 are connected to each otherthrough a gas hydrate slurry return pipe 59. A pump 60 and a flowregulating valve 61 are provided to the gas hydrate slurry return pipe59. The flow regulating valve 61 is controlled by means of an NGHpercentage meter 62 provided to the gas hydrate slurry discharge pipe58.

Moreover, a raw-material-gas supply pipe 63 and a raw-material-watersupply pipe 64 are provided to the first mixer 51. Furthermore, araw-material-gas supply pipe 63 a branched from the raw-material-gassupply pipe 63 is provided to the second mixer 55. Note that thestructure of each of the first mixer 51 and the second mixer 55 is thesame as that of the mixer 1 in the first embodiment, and thus detaileddescription thereof will be omitted. Also, the structure of each of thefirst generator 53 and the second generator 57 is the same as that ofthe generator 2 in the first embodiment, and thus detailed descriptionthereof will be omitted.

Next, the operation of the gas hydrate production apparatus of thisembodiment will be described.

As illustrated in FIG. 8, a raw-material water w that has been cooled toa predetermined temperature (for example, 4 to 8° C.) and a raw-materialgas g that has been pressurized up to a predetermined pressure (forexample, 4 to 5.5 MPa) are supplied to the ejector-type first mixer 51.At this time, the raw-material gas g is formed into fine bubbles, whichare then mixed uniformly with the raw-material water w. A mixed water w′into which the raw-material gas g has been mixed flows through the firstpipe 52 to be supplied to the shell-and-tube-type first generator 53.The mixed water w′ thus supplied to the first generator 53 undergoesreaction to form minute gas hydrate cores while meandering forward andbackward inside the shell-and-tube type first generator 53.

A slurry S (having an NGH percentage of 1 to 5%) containing the gashydrate cores formed in the first generator 53 flows through the secondpipe 54 to be supplied to the second mixer 55. The second pipe 548located between a slurry pump 65 and the second mixer 55 branches at abranching point b, and is thus configured so that a part of the slurryis injected into the first pipe 52 through a branch pipe 66. Here, theamount of the slurry to be circulated may be approximately 0 to 10%.

Since the raw-material gas g is supplied to the second mixer 55 from theraw-material-gas supply pipe 63 a, the slurry S and the raw-material gasg are stirred and mixed by the second mixer 55. A slurry S′ thussupplied with the raw-material gas g flows through the third pipe 56 tobe supplied to the shell-and-tube-type second generator 57. The slurryS′ supplied to the second generator 57 undergoes reaction to form a gashydrate slurry s while meandering forward and backward inside theshell-and-tube-type second generator 57 having a cooling temperature setat, for example, 1 to 7° C.

The gas hydrate slurry s thus generated by the second generator 57 isdischarged to the next process through the gas hydrate slurry dischargepipe 58. In the meantime, the NGH percentage of the gas hydrate slurry scan be controlled (for example, at 20 to 30%) by controlling the flowregulating valve 61 by means of the NGH percentage meter 62 provided tothe gas hydrate slurry discharge pipe 58.

Moreover, since a part of the gas hydrate slurry s generated by thesecond generator 57 is returned to the upstream of the second mixer 55through the gas hydrate slurry return pipe 59, the crystallization ofthe gas hydrate is promoted, so that the particles of the gas hydratecan be increased in size.

1. A gas hydrate production apparatus characterized by comprising: anejector-type mixer that stirs and mixes a raw-material gas and araw-material water; a shell-and-tube-type generator provided downstreamof the ejector-type mixer; partition walls provided in end plates placedrespectively in the front and rear ends of the generator, the partitionwalls each causing a gas hydrate slurry to turn around; a dehydratorprovided downstream of the generator, the dehydrator including acone-shaped filter; a drainage pipe provided to the dehydrator; and aflow regulating valve provided to the drainage pipe.
 2. A gas hydrateproduction apparatus characterized by comprising: an ejector-type firstmixer that stirs and mixes a raw-material gas and a raw-material water;a shell-and-tube-type first generator provided downstream of theejector-type first mixer, the first generator intended to generate gashydrate cores; an ejector-type second mixer provided downstream of thefirst generator, the second mixer mixing the raw-material gas into aslurry containing the gas hydrate cores, and then stirring and mixingthe raw-material gas and the slurry; a second generator provideddownstream of the second mixer, the second generator intended togenerate a gas hydrate; and a flow regulating valve provided to a pipethrough which a part of the gas hydrate slurry generated by the secondgenerator is returned to the second mixer.
 3. The gas hydrate productionapparatus according to claim 2, characterized in that partition wallsare provided in each of end plates placed respectively in the front andrear ends of each of the first and second generators, the partitionwalls each causing the slurry to turn around.
 4. The gas hydrateproduction apparatus according to claim 1, characterized in that cornerportions are provided among joint portions of each end plate and thecorresponding partition walls, the corner portions each having a curvedwettable surface.
 5. The gas hydrate production apparatus according toclaim 1, characterized in that first collision bodies and secondcollision bodies are provided alternately in a narrowly constricted bodyportion of each ejector type mixer, the first collision bodies eachbeing a plate-shaped base plate provided with triangular or trapezoidalpenetrating portions radially formed therein, the second collisionbodies each being a plate-shaped base plate provided with a stellatepenetrating portion formed therein.
 6. The gas hydrate productionapparatus according to claim 1, characterized in that a part of the gashydrate slurry generated by the generator is returned and recirculatedto the generator.
 7. The gas hydrate production apparatus according toclaim 2, characterized in that a part of the gas hydrate slurrygenerated by the first generator is returned and recirculated to thefirst generator.